1. Field of the Invention
The invention relates to a fluid filter. More particularly, the invention relates to a fluid filter, for example, a fuel filter, that has a collection chamber for collecting water separated out from the fuel and a liquid sensor.
2. Description of the Prior Art
Fluid filters with a collecting chamber below the filter medium are known in practice, for example, in the form of fuel filters for combustion engines, particularly as diesel fuel filters for vehicular engines. The fluid to be filtered is thereby the fuel, and the liquid that is to be separated out into the collecting chamber is water. For example, water can get into the fuel, if water from condensation forms in the fuel tank.
In such fluid filters, the filter medium is hydrophobic or is constructed in another way to be water-impermeable, so that the filter insert not only serves to cleanse the fuel of impurities, but also functions as a water separator. The liquid separated out by the filter insert, e.g., water, collects in a collecting chamber below the filter insert.
First of all, the filter itself must be protected from an excessively large amount of collected water: for example, if the filter insert were to constantly stand in water, the filter medium, for example, a paper filter medium, could be damaged; furthermore, the filtering surface available for filtering the fuel would be reduced if the liquid level of the water were too high. Secondly, damage could occur to the combustion engine or the fuel injection system if, due to an excessively high water level in the collecting chamber of the fluid filter, an impermissibly high amount of water were to be delivered with the fuel.
For this reason, it is known to provide a liquid sensor, namely, a water sensor, in the collecting chamber of the fuel filter. The water has a higher specific weight than the fuel. It therefore collects below the fuel or displaces the fuel, which is found at the bottom of the collecting chamber. Additional amounts of water reaching the collecting chamber cause the water level in the collecting chamber to rise.
As soon as the water reaches an excessively high liquid level in the collecting chamber, an alarm is sent, for example, to the operator of the motor or the driver of the vehicle. Alternatively or in addition to this, a protective measure for the combustion engine can be initiated automatically by means of the engine control, for example, a switch-over to an emergency operating system that requires less fuel delivery, whereby the available motor power is clearly reduced, a side effect that is noticeable to the driver of the vehicle.
In practice, it cannot be excluded that there is not only an overall rise in the liquid level in the collecting chamber, but also that apart from the fill volume in the collecting chamber, the liquid in the chamber is subject to centrifugal forces that cause it to slosh back and forth, for example, when the vehicle drives into corners or curves or over bumps on an uneven road surface. As a result, the liquid can come into contact with the liquid sensor before the amount of liquid in the collecting chamber has reached what is considered to be a critical fill volume. In such a situation, the liquid sensor therefore emits a fill level signal that is characterized as erroneous information or faulty signaling within the context of the present proposal, because the registered contact of the liquid sensor with the liquid does not correspond to the actual liquid level within the collecting chamber.
DE 101 35 592 A1 discloses a generic fluid filter in the form of a fuel filter. In this fuel filter, the liquid sensor is surrounded by a hat-shaped closer, the upper end of which forms a collar-like ring flange, and which has several windows in its circumferential walls and forms a seal with its lower frontal surface resting on a flat gasket. When the liquid sensor is removed, the closer, which is spring biased, is raised, so that water from the collecting chamber flows out past the flat gasket, thus enabling the collecting chamber to be emptied. This closer is not provided as a protective wall against fluctuating liquid levels due to sloshing water. It is rather a part of a closure or valve that automatically opens when the water sensor is removed, so that now water can automatically flow out of the collecting chamber through the opened valve.
As expressly mentioned in DE 101 35 592 A1, with the water sensor removed, the resulting opening enables air to flow into the housing from the outside and water to flow off unimpeded. It is, however, certainly not clear in DE 101 35 592 A1 how, with the liquid sensor installed, water, which passes through the windows into the interior space of the hat-shaped closer, could reach the water sensor, in order to moisten the sensor contact there and thus trigger the desired alarm signal.
The interior space surrounded by the hat-shaped closer is, namely, closed toward the top and has the aforementioned windows only below the sensor contacts. Ingress of water through the windows can certainly displace the fuel that is found at the window level in this interior space. It is, however, not possible that the water level in the interior space of the closer will continue to rise, because the fuel does not represent a compressible medium, and in any case is not appreciably compressible under the pressures of ca. 8 bars that typically prevail in a fuel filter.
The closer is not provided as a protective wall against fluctuating liquid levels caused by sloshing water, because merely this single wall, in the form of the hat-shaped closer, is provided between the interior space where the water sensor is located and the surrounding water collecting chamber, and several windows are provided in this closer, and, as DE 101 35 592 A1 expressly mentions, the windows are supposed to enable the free flow of water. Furthermore, because they are supposed to be arranged explicitly evenly distributed around the periphery of the closer, impeding the water flow is neither intended nor even at all possible.
The object of the invention is to improve a generic fluid filter that provides the most trouble-free operation possible of a combustion engine in cooperation with a fluid filter and that avoids erroneous liquid sensor information. An additional object of the invention is to specify a filter insert suitable for such a fluid filter.